Cathode composite material and lithium ion battery using the same

ABSTRACT

A cathode composite material includes a cathode active material and a coating layer coated on a surface of the cathode active material. The cathode active material includes a spinel type lithium manganese oxide. The coating layer comprises a lithium metal oxide having a crystal structure belonging to C2/c space group of the monoclinic crystal system. The present disclosure also relates to a lithium ion battery including the cathode composite material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201210373521.2, filed on Sep. 27, 2012 inthe China Intellectual Property Office, the content of which is herebyincorporated by reference. This application is related tocommonly-assigned applications entitled, “CATHODE COMPOSITE MATERIAL,METHOD FOR MAKING THE SAME, AND LITHIUM ION BATTERY USING THE SAME”,filed ______ (Atty. Docket No. US47009); “CATHODE COMPOSITE MATERIAL,METHOD FOR MAKING THE SAME, AND LITHIUM ION BATTERY USING THE SAME”,filed ______ (Atty. Docket No. US47008); “CATHODE COMPOSITE MATERIAL ANDLITHIUM ION BATTERY USING THE SAME”, filed ______ (Atty. Docket No.US47013); “CATHODE COMPOSITE MATERIAL AND LITHIUM ION BATTERY USING THESAME”, filed ______ (Atty. Docket No. US47016); “CATHODE COMPOSITEMATERIAL AND LITHIUM ION BATTERY USING THE SAME”, filed ______ (Atty.Docket No. US47017); “CATHODE COMPOSITE MATERIAL AND LITHIUM ION BATTERYUSING THE SAME”, FILED ______ (Atty. Docket No. US47018).

BACKGROUND

1. Technical Field

The present disclosure relates to cathode active materials used inrechargeable lithium ion batteries, and particularly to a cathodecomposite material, and a rechargeable lithium ion battery using thesame.

2. Description of Related Art

Lithium ion batteries can experience capacity loss during charging anddischarging cycles and a poor cycling life due to the capacity loss. Onereason for the capacity loss during the cycling is an un-reversiblechange of an intrinsic structure of a cathode active material thatoccurs during cycling. Another reason for the capacity loss during thecycling is a cathode active material loss caused by a reaction betweenthe cathode active material and the organic solvent that occurs when thecathode active material is in a lithium ion deintercalation state andthus has a high oxidability. Therefore, how to improve the stability ofthe cathode active material during cycling of the battery and decreaseunwanted reactions in the battery is crucial in improving the cyclinglife of the lithium ion battery.

A common method to improve the conductive properties of cathode activematerials of lithium batteries is to treat the surface of the materials.For example, compared to untreated LiFePO₄, the carbon coated LiFePO₄particles has improved conductivity. However, the stability improvingproblem during the cycling of the lithium ion battery has not beenproperly solved.

What is needed, therefore, is to provide a cathode composite materialhaving a relatively good cycling stability and a lithium ion batteryusing the same.

BRIEF DESCRIPTION OF THE DRAWING

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, the emphasis instead being placed upon clearlyillustrating the principles of the present embodiments.

FIG. 1 is a view of an embodiment of a cathode composite material of alithium ion battery.

FIG. 2 is a view of an embodiment of a method for making the cathodecomposite material of the lithium ion battery.

FIG. 3 is a view of an embodiment of a method for making a compositeprecursor in the method for making the cathode composite material of thelithium ion battery.

FIG. 4 shows an XRD pattern of Mn doped Li₂TiO₃ coated LiMn₂O₄ ofExample 1.

FIG. 5 is a graph comparing cycle performance testing results indifferent current rates of lithium ion batteries of Example 1 andComparative Example 1.

FIG. 6 is a graph comparing cycle performance testing results of lithiumion batteries of Example 1 and Comparative Example 1.

FIG. 7 is a cross-sectional view of an embodiment of a lithium ionbattery.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “another,” “an,” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

Referring to FIG. 1, one embodiment of a cathode composite material 10of a lithium ion battery includes a cathode active material particle 12and a coating layer 14 coated on a surface of the cathode activematerial particle 12.

Cathode Active Material

The cathode active material particle 12 can be any commonly used cathodeactive material of lithium ion battery. For example, the material of thecathode active material particle 12 can be a lithium transition metaloxide. The transition metal of the lithium transition metal oxide can beat least one of cobalt (Co), nickel (Ni), and manganese (Mn). Thelithium transition metal oxide can have a crystal structure of spineltype, layered type, or olivine type. In one embodiment, the lithiumtransition metal oxide can be a spinel type lithium manganese oxide.

The spinel type lithium manganese oxide can be represented by a chemicalformula of Li_(x)Mn_(2-z)L_(z)O₄, wherein 0.1≦x≦1.1, 0≦z<2. In oneembodiment, 0.1<z<0.5. L represents at least one of the chemicalelements of alkali metal elements, alkaline-earth metal elements,Group-13 elements, Group-14 elements, transition metal elements, andrare-earth elements. In one embodiment, L represents at least one of thechemical elements of Co, Ni, chromium (Cr), vanadium (V), titanium (Ti),tin (Sn), copper (Cu), aluminum (Al), iron (Fe), boron (B), strontium(Sr), calcium (Ca), gallium (Ga), neodymium (Nd), and magnesium (Mg). Inone embodiment, y=0, and the formula is LiMn₂O₄.

The shape of cathode active material particle 12 is not limited and canbe sphere shape, rod shape, needle shape, sheet shape, tube shape, orirregular shape. A cathode electrode of a lithium ion battery caninclude a plurality of cathode active material particles 12 in a powderform.

The size of a single cathode active material particle 12 can be chosenaccording to need and can be in a range from about 1 micron to about 500microns.

Coating Layer

The coating layer 14 can be an in situ formed layer on the surface ofthe cathode active material particle 12 and can be a continuous materiallayer having a uniform thickness. The material of the coating layer 14can be a lithium metal oxide having a crystal structure belonging toC2/c space group of the monoclinic crystal system. A general chemicalformula of the lithium metal oxide can be Li₂AO₃, wherein A represents ametal element which has a +4 valence. In one embodiment, the A of theLi₂AO₃ can be selected from at least one of Ti, Sn, Mn, lead (Pb),tellurium (Te), ruthenium (Ru), hafnium (Hf), and zirconium (Zr). Forexample, the lithium metal oxide can be at least one of Li₂TiO₃,Li₂MnO₃, Li₂SnO₃, Li₂PbO₃, Li₂TeO₃, Li₂RuO₃, Li₂HfO₃, and Li₂ZrO₃.

The lithium metal oxide can be undoped, or doped with doping chemicalelements. The transition metal atoms of the cathode active material 12can diffuse into the coating layer 14 to form the doped lithium metaloxide. The lithium metal oxide can also be represented by a generalformula of[Li_(1-2a)M_(a)□_(a)][Li_(1/3-2b-c)M_(b)N_(3c)A_(2/3-2c)□_(b)]O₂,wherein M and N represent doping chemical elements, “□” represents anatom vacancy, which occupies a Li site in the [Li][Li_(1/3)A_(2/3)]O₂,0≦2a<1, 0≦2b+c<⅓, and 0≦2c<⅔. In the general formula, atoms of Li_(1-2a)M_(a)□_(a) are located on inter-plane octahedral sites, atoms ofLi_(1/3-2b-c)M_(b)N_(3c)A_(2/3-2c)□_(b) are located on in-planeoctahedral sites. More specifically, the undoped Li₂AO₃ can also berepresented by the chemical formula of [Li]^(α)[Li_(1/3)A_(2/3)]^(β)O₂,which is a transform of the formula Li₂AO₃, wherein [ ]^(α) representsthat the atoms in the [ ]^(α) are located on the inter-plane octahedralsites, which are occupied by Li, and [ ]^(β) represents that the atomsin the [ ]^(β) are located on the in-plane octahedral sites, which areoccupied by Li and A in a molar ratio of ⅓:⅔. When the ions of thedoping element M replace an amount of Li⁺ located on the inter-planeoctahedral sites and in-plane octahedral sites, an equal amount of atomvacancies (□) are also generated. The atom vacancies (□) are helpful forLi⁺ moving in the coating layer 14. Further, the ions of the dopingelement N can replace an amount of Li⁺ and A⁴⁺ of the Li_(1/3)A_(2/3)located on the in-plane octahedral sites.

More specifically, M and N respectively represent at least one of thechemical elements of alkali metal elements, alkaline-earth metalelements, Group-13 elements, Group-14 elements, transition metalelements, and rare-earth elements. In one embodiment, M and Nrespectively represent at least one of the chemical elements of Co, Mn,Ni, Cr, V, Ti, Sn, Cu, Al, Fe, B, Sr, Ca, Ga, Nd, and Mg.

At least one of M and N can come from the lithium transition metal oxideof the cathode active material particle 12. When the lithium transitionmetal oxide is the lithium manganese oxide, at least one of M and N canbe Mn. For example, when N is Mn, the general formula of the material ofthe coating layer can be [Li][Li_(1/3-c)Mn_(3c)A_(2/3-2c)]O₂. When A isTi, the general formula of the material of the coating layer can be[Li][Li_(1/3-c)Mn_(3c)Ti_(2/3-2c)]O₂.

A mass percentage of the coating layer 14 to the cathode compositematerial 10 can be in a range from about 0.05% to about 7%. In oneembodiment, the mass percentage of the coating layer 14 is about 5%. Athickness of the coating layer 14 can be in a range from about 2nanometers (nm) to about 20 nm.

The cathode electrode of the lithium ion battery can include a pluralityof cathode active material particle 12. The coating layer 14 can beindividually coated on the individual cathode active material particle12. The cathode electrode of the lithium ion battery can include aplurality of core-shell structures. Each core-shell structure has onecathode active material particle 12 as the core and one coating layer 14as the shell. In one embodiment, each of the plurality of cathode activematerial particle 12 in the cathode electrode has the coating layer 14coated thereon. The coating layer 14 can completely coat an entire outersurface of the individual cathode active material particle 12. Thecoating layer 14 can have a uniform thickness, and thus the cathodecomposite material 10 can have a sphere shape, rod shape, needle shape,sheet shape, tube shape, or irregular shape corresponding to the shapeof the cathode active material particle 12.

Method for Making the Cathode Active Material

One embodiment of a method for preparing the cathode composite materialof the lithium ion battery includes steps of:

-   -   S1, forming a composite precursor including a cathode active        material precursor and a coating layer precursor coated on a        surface of the cathode active material precursor;    -   S2, reacting the composite precursor with a lithium source        chemical compound, to lithiate both the cathode active material        precursor and the coating layer precursor in the composite        precursor.

The cathode active material precursor is capable of having a chemicalreaction with the lithium source chemical compound to produce thecathode active material. In one embodiment, the cathode active materialprecursor is capable of having a chemical reaction with the lithiumsource chemical compound to produce the spinel type lithium manganeseoxide. The cathode active material precursor is used as a manganesesource. The material of the cathode active material precursor can be anoxygen compound of the manganese. The oxygen compound can be at leastone of hydroxides, oxysalts, and oxides of manganese. The oxysalt is asalt of an oxyacid. The oxysalt can be at least one of oxalates,carbonates, acetates, and oxyhydroxides (i.e., oxide-hydroxides). Forexample, the oxysalt of the transition metal can be at least one ofmanganese hydroxide (Mn(OH)₂), manganese oxalate (MnC₂O₄.2H₂O),manganese carbonate (MnCO₃), manganese acetate (Mn(CH₃COO)₂.4H₂O), andmanganese oxide-hydroxide (MnOOH). The oxygen compound of the manganesecan be with or without the crystallization water.

The material of the coating layer precursor can be hydroxides or oxidesof the metal element which has the +4 valence. For example, the materialof the coating layer precursor can be at least one of titanium dioxide(TiO₂), stannic dioxide (SnO₂), manganese dioxide (MnO₂), lead dioxide(PbO₂), tellurium dioxide (TeO₂), ruthenium dioxide (RuO₂), hafniumdioxide (HfO₂), and zirconium dioxide (ZrO₂).

The material of the lithium source chemical compound can be at least oneof lithium hydroxide, lithium chloride, lithium sulfate, lithiumnitrate, lithium acetate, lithium dihydrogen orthophosphate.

Referring to FIG. 2, the above described method can be used to form thecathode composite material 10. The composite precursor 100 can includethe coating layer precursor 140 and the cathode active materialprecursor 120. The coating layer precursor 140 is coated on the cathodeactive material precursor 120. The coating layer precursor 140 iscapable of having a chemical reaction with the lithium source chemicalcompound to produce the coating layer 14. That is to say, the coatinglayer precursor 140 is a chemical compound which can have a chemicalreaction with the lithium source chemical compound to produce thelithium metal oxide having a crystal structure belonging to the C2/cspace group of the monoclinic crystal system. The cathode activematerial precursor 120 is capable of having a chemical reaction with thelithium source chemical compound to produce the cathode active materialparticle 12. The coating layer precursor 140 is a continuous layershaped structure, which is in-situ formed on the outer surface of thecathode active material precursor 120. The lithium source chemicalcompound 160 can simultaneously react with the cathode active materialprecursor 120 and the coating layer precursor 140, to produce thecathode active material particle 12 and the coating layer 14 coated onthe cathode active material particle 12. The cathode active materialprecursor 120 can have a particle shape. In one embodiment, a pluralityof cathode active material precursors 120 are provided, and the coatinglayer precursor 140 is individually coated on the individual cathodeactive material precursor 120.

In one embodiment, the step S1 can further include steps of:

S11, dispersing the plurality of cathode active material precursors in aliquid solvent to form a solid-liquid mixture, and the plurality ofcathode active material precursors are insoluble to the liquid solvent;

S12, adding a coating substance in the solid-liquid mixture;

S13, heating the solid-liquid mixture having the coating substance addedtherein to form the coating substance into the coating layer precursoron the outer surface of the cathode active material precursor, therebyforming the composite precursor.

In one embodiment, when the oxygen compound of the manganese is at leastone of manganese hydroxides and manganese oxysalts, or when the oxygencompound of the manganese carries the crystallization water, the liquidsolvent can only be an organic solvent (i.e., without water). Themanganese hydroxides, manganese oxysalts, or the crystallization watercan generate water in the solid-liquid mixture due to the heating step.The water reacts with the coating substance. The organic solvent can bea commonly used solvent such as methanol, ethanol, propanol,isopropanol, ethylene glycol, acetone, dichloroethane, and chloroform.

The coating substance can be a liquid state substance, a liquidsolution, or a substance that is soluble to the liquid solvent. Thecoating substance can include at least one of metal halides and metalesters. In one embodiment, the metal element in the metal halides andmetal esters has the +4 valence. More specifically, the coatingsubstance can be at least one of diethyl titanate, tetrabutyl titanate,zirconium n-butoxide, tetrabutyl orthostannate, titanium tetrachloride(TiCl₄), zirconium tetrachloride (ZrCl₄), stannic tetrachloride (SnCl₄),lead tetrachloride (PbCl₄), tellurium tetrachloride (TeCl₄), rutheniumtetrachloride (RuCl₄), hafnium tetrachloride (HfCl₄), manganesetetrachloride (MnCl₄).

In the step S11, the plurality of cathode active material precursor canbe uniformly dissolved in the liquid solvent through an ultrasonicvibration or a mechanical stirring method.

In the step S12, a molar ratio of the coating substance to the cathodeactive material precursor can be in a range from about 0.1:100 to about20:100. The coating substance can be uniformly mixed with thesolid-liquid mixture through an ultrasonic vibration or a mechanicalstirring method.

In the step S13, the liquid-solid mixture having the coating substanceadded therein can be directly heated in an open environment in air orheated by using a hydrothermal synthesis method in an autoclave, whichis sealed and has a pressure larger than 1 atm therein during theheating. The heating temperature can be decided according to thepressure and the material of the coating substance. In one embodiment,the heating temperature can be in a range from about 80° C. to about200° C. The heating time can be decided according to the heatingtemperature and the amount of the coating substance. In one embodiment,the heating time can be in a range from about 10 minutes to about 20hours. In the heating step of the step S13, the coating substance canhave a hydrolysis reaction to produce the coating layer precursor on theouter surface of the cathode active material precursor.

Referring to FIG. 3, when the cathode active material precursor 120carries the crystallization water 180, during the heating step of thestep S13, the crystallization water can escape from the cathode activematerial precursor 120 to form a liquid state water. The liquid statewater can have a reaction with the coating substance 144 to form thecoating layer precursor 140 coated on the surface of the crystallizationwater removed cathode active material precursor 120′.

By using the liquid solvent without the water, and providing the wateronly by the crystallization water of the cathode active materialprecursor, the reaction between the water and the coating substance iseasier to be controlled and the morphology of the coating layerprecursor can be formed well. Accordingly, the uniformity of the coatinglayer precursor can be improved.

In another embodiment, the step S1 can include steps of:

S11′, dispersing the plurality of cathode active material precursor in aliquid solvent to form a solid-liquid mixture, and the plurality ofcathode active material precursor is insoluble to the liquid solvent.

S12′, adding a coating substance in the solid-liquid mixture;

S13′, reacting the coating substance with water to have a hydrolysisreaction, to produce the coating layer precursor on the outer surface ofthe cathode active material precursor, thereby forming the compositeprecursor.

The steps S11′ to S13′ is similar to the steps S11 to S13, except thatwhen the cathode active material precursor 120 itself does not carriesthe crystallization water, an additional step of reacting the coatingsubstance with an added water can be used to hydrolyses the coatingsubstance. More specifically, in one embodiment, the liquid solvent canbe a mixture of the organic solvent and a small amount of water. Avolume ratio between the water and the organic solvent can be equal toor smaller than 1:10 (in some embodiments is smaller than 1:50). Inanother embodiment, when the liquid solvent only includes the organicsolvent, the step S13′ can further include a step of adding water intothe solid-liquid mixture. The amount of the added water can be decidedby the amount of the coating substance. Overall, the solid-liquidmixture can include a small amount of water. The amount of the water canbe decided by the amount of the coating substance.

In the step S2, the composite precursor is reacted with the lithiumsource chemical compound, the cathode active material precursor and thecoating layer precursor can both be lithiated. A high-temperaturesolid-state reaction can be used to react the composite precursor withthe lithium source chemical compound. More specifically, the step S2 caninclude steps of uniformly mixing the composite precursor with thelithium source chemical compound to form a solid-solid mixture andheating the solid-solid mixture, under a solid-state reactiontemperature. The composite precursor and the lithium source chemicalcompound can be mixed through a mechanical stirring method or a ballmilling method. The solid-state reaction temperature can be decidedaccording to the material of the composite precursor. In one embodiment,the solid-state reaction temperature can be in a range from about 400°C. to about 900° C., and the heating time can be in a range from about 2hours to about 12 hours.

In one embodiment, before heating the solid-solid mixture under thesolid-state reaction temperature, an additional step of pre-heating thesolid-solid mixture under a relatively low temperature can be processedfor fully decomposing the composite precursor. The relatively lowtemperature can be in a range from about 350° C. to about 400° C., andthe pre-heating time can be in a range from about 0.5 hours to about 1hour. After the pre-heating step, the solid-solid mixture can bedirectly heated to reach the solid-state reaction temperature without acooling step.

An amount of the lithium source chemical compound can be decided by theamount of the composite precursor. More specifically, the amount of thelithium source chemical compound can be calculated from the lithiumamount required for lithiating the cathode active material precursor andthe coating layer precursor. Moreover, for the reason that the lithiumis apt to be volatilized in a high temperature, the lithium sourcechemical compound can be excess for the composite precursor. In oneembodiment, the stoichiometric ratio between the lithium source chemicalcompound and the composite precursor can be in a range from about 1:1 toabout 1.2:1. During the lithiation of the cathode active materialprecursor to produce the cathode active material, the lithium sourcechemical compound also reacts with the coating layer precursor, anddirectly forms the coating layer on the surface of the formed cathodeactive material. The coating layer precursor and the cathode activematerial precursor are simultaneously heated at the solid state reactiontemperature, and both form the lithiated substances; thus, there is astrong chemical bonding force between the formed cathode active materialand the coating layer, to make the coating layer continuously, tightlyand uniformly coated on the surface of the cathode active material.

It is to be understood that the coating substance can include more thanone metal elements which having the +4 valence. Thus, the finally formedcoating layer 14 can include more than one lithium metal oxide mixedwith each other. Moreover, the cathode active material precursor canalso include more than one oxygen compounds of the transition metals.Thus, the finally formed cathode active material particle 12 can includemore than one transition metal elements. Moreover, the cathode activematerial precursor can also include at least one of the above mentioneddoping elements L. Thus, the finally formed cathode active materialparticle 12 can be a doped lithium transition metal oxide, for example,a doped spinel type lithium manganese oxide.

The cathode composite material of the present disclosure includes thecoating layer coated on the cathode active material to avoid a directcontact between the cathode active material and the electrolytesolution. The material of the coating layer can be a lithium metal oxidehaving a crystal structure belonging to C2/c space group of themonoclinic crystal system. Thus, the lithium metal oxide has a onedimensional lithium ion transferring path along a crystal axis c of thecrystal structure of the lithium metal oxide. Therefore, the coatinglayer can prevent an electron migration between the electrolyte and thecathode active material and allow the lithium ions to pass therethrough.Thus, the side reaction during the charge and discharge of the lithiumion battery between the electrolyte and the cathode active material canbe suppressed. Therefore, the cathode composite material has improvedchemical and thermal stabilities, even at a relatively high or lowcharge/discharge voltage, or a high rate.

In an embodiment of the method, a composite precursor having acore-shell structure is previously prepared, and then the core and theshell of the core-shell structure are simultaneously lithiated, to formthe cathode composite material and the cathode active material at thesame time. The in situ formed coating layer is an integrated andcontinuous material layer having uniform thickness, not just a pluralityof particles loosely stacked on the cathode active material. The coatinglayer and the cathode active material have a tight combination, whicheffectively decreases the dislocation and increase the lithium ionmobility in the coating layer. Therefore, the lithium ion battery usingthe cathode composite material has a relatively good cycle performance.

Lithium Ion Battery

Referring to FIG. 7, one embodiment of a lithium ion battery 1 includesa cathode electrode 2, an anode electrode 3 spaced from the cathodeelectrode 2, and a non-aqueous electrolyte 8 disposed between thecathode electrode 2 and the anode electrode 3.

The cathode electrode 2 can include a cathode current collector 24 and acathode material layer 22. The cathode current collector 24 is used forsupporting the cathode material layer 22 and conducting current. A shapeof the cathode current collector 24 can be a continuous sheet or anetwork. A material of the cathode current collector 24 can be metal oralloy, such as aluminum, titanium, or stainless steel. The cathodematerial layer 22 is disposed on at least one surface of the cathodecurrent collector 24. The cathode material layer 22 includes the abovedescribed cathode composite material 10 and can further include aconductive agent and a binder. The cathode composite material 10,conductive agent, and the binder can be uniformly mixed with each other.

The anode electrode 3 can include an anode current collector 34 and ananode material layer 32. The anode current collector 34 is used forsupporting the anode material layer 32 and conducting current. A shapeof the anode current collector 34 can be a continuous sheet or anetwork. A material of the anode current collector 34 can be metal oralloy, such as copper, nickel, or stainless steel. The anode materiallayer 32 is disposed on at least one surface of the anode currentcollector 34. The anode material layer 32 includes an anode activematerial and can further include a conductive agent and a binder. Theanode active material, conductive agent, and the binder can be uniformlymixed with each other. The anode active material particle can be lithiumtitanate (e.g., Li₄Ti₅O₁₂), graphite, acetylene black, organic crackingcarbon, mesocarbon microbeads (MCMB), or any combination thereof.

The anode material layer 32 faces the cathode material layer 22. Boththe anode material layer 32 and the cathode material layer 22 are incontact with the electrolyte. The electrolyte 8 can be a solidelectrolyte film or a liquid non-aqueous electrolyte solution. The solidelectrolyte film can be sandwiched between the anode electrode 3 and thecathode electrode 2. If the lithium ion battery 1 uses the liquidnon-aqueous electrolyte solution, the cathode electrode 2 and the anodeelectrode 3 are both disposed in the liquid non-aqueous electrolytesolution. The lithium ion battery 1 can further include a separator 4disposed between the anode material layer 32 and the cathode materiallayer 22, to electrically insulate them from each other. The separator 4is capable of having the lithium ions pass therethrough. The liquidnon-aqueous electrolyte solution includes an organic solvent and alithium salt dissolved in the organic solvent. The organic solvent canbe selected from cyclic carbonates, linear carbonates, cyclic ethers,linear ethers, nitriles, and amides, and can be at least one of ethylenecarbonate (EC), propylene carbonate (PC), ethylmethyl carbonate (EMC),diethyl carbonate (DEC), dimethyl carbonate (DMC), butylenes carbonate,vinylene carbonate, methylethyl carbonate, methyl acetate, ethylacetate, propyl acetate, methyl propionate, ethyl propionate,y-butyrolactone, 1,2dimethoxyethane, 1,2-diethoxyethane,tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran, acetonitrile, anddimethylformamide. The lithium salt may be at least one of LiPF₆, LiBOB,LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, LiC₄F₉SO₃,LiSbF₆, LiAlO₄, LiAlCl₄, LiCl, and LiI. The separator 4 can be a porousmembrane. The material of the separator can be polyolefins, such aspolypropylene (PP) or polyethylene (PE), or inorganic material such asporous ceramics.

The conductive agents and the binders in the anode material layer 32 andthe cathode material layer 22 can be the same. The conductive agent canbe a carbonaceous material such as carbon black, acetylene black,conductive polymers, carbon fibers, carbon nanotubes, graphene, andgraphite. The binder can be at least one of polyvinylidene fluoride(PVDF), polytetrafluoroethylene (PTFE), and styrene-butadiene rubber(SBR).

The materials of the anode current collector 34, the cathode currentcollector 24, the conductive agent, the binder, the electrolyte, and theseparator 4 are not limited by the above listed materials, and can beselected from other known materials.

The lithium ion battery 1 can further include an exterior encapsulatingstructure, such as a hard battery case 5 sealed by a sealing member 6,or a soft encapsulating bag, having the cathode electrode 2, the anodeelectrode 3, the separator 4, the electrolyte 8 located therein. Thelithium ion battery 1 can further include a connecting componentachieving an electrical connection between the current collector of thelithium ion battery 1 and the external circuit.

EXAMPLES Example 1

In Example 1, 0.25 g MnOOH is ultrasonically dispersed in 10 mL ofethanol to achieve the solid-liquid mixture. Then, the tetrabutyltitanate is added into the solid-liquid mixture. A molar percentage ofthe tetrabutyl titanate to the MnOOH is about 5%. After adding thetetrabutyl titanate, the solid-liquid mixture is continuouslyultrasonically vibrated to uniformly mix the tetrabutyl titanate and theMnOOH in the ethanol. After that, the solid-liquid mixture istransferred into a dry and clean hydrothermal autoclave and reacted atabout 150° C. for about 3 hours. After the hydrothermal synthesis, theamorphous TiO₂ layer can be formed on the surface of the MnOOH, to formthe composite precursor. The composite precursor and the LiOH.H₂O aremixed in the stoichiometric ratio and are dried to remove the residualethanol. Then the mixture of the composite precursor and the LiOH.H₂Oare heated to about 800° C. at a temperature increasing rate of about 3°C./min and is maintained at the 800° C. for about 5 hours. The cathodecomposite material is naturally cooled down to room temperature. Thecathode composite material is the core-shell structure having LiMn₂O₄ asthe core and Mn doped Li₂TiO₃ as the shell. An XRD analysis is conductedon the cathode composite material. Referring to FIG. 4, the XRD patternof the cathode composite material shows that a pure phase LiMn₂O₄ exitsin the cathode composite material. The peak of the Li₂TiO₃ disappears,which means that Mn ions are doped in the Li₂TiO₃. An X-rayphotoelectron spectroscopy (XPS) analysis is conducted on the cathodecomposite material to measure the content of the element on the surfaceof the cathode composite material. The XPS analysis result shows thatthe molar percentage of Ti element is about 15.29%, which is much largerthan 5%. That is, Ti element mainly exists on the surface of the cathodecomposite material. According to a further calculation, Ti element onlyexist on an outer surface layer having a thickness of about 10 nm of thecathode composite material.

A lithium ion battery is assembled using the cathode composite materialof the Example 1 in the cathode electrode.

Comparative Example 1

A lithium ion battery is assembled according to the same conditions asin Example 1, except that the cathode composite material formed inExample 1 is replaced by the bare LiMn₂O₄ without any coating layercoated thereon.

Electrochemical Experiment of Example 1 and Comparative Example 1

Referring to FIG. 5, the two lithium ion batteries of the Example 1 andComparative Example 1 are galvanostatically cycled using the currentrates of 0.5 C, 1 C, 3 C, and 7 C. As the current rate increases, thedischarge specific capacity of the lithium ion battery of theComparative Example 1 dramatically decreases. When the current rate getsto 7 C, the discharge capacity of the lithium ion battery of theComparative Example 1 is only about 20 mAh/g. On the contrary, thelithium ion battery in the Example 1 having the LiMn₂O₄ coated by the Mndoped Li₂TiO₃ coating layer has a much better rating performance. As thecurrent rate increases, the discharge specific capacity of the lithiumion battery of the Example 1 does not decrease much. When the currentrate gets to 7 C, the discharge specific capacity of the lithium ionbattery of the Example 1 is still about 40 mAh/g.

Referring to FIG. 6, the two lithium ion batteries of the Example 1 andComparative Example 1 are galvanostatically cycled using a current rateof 5 C at a temperature of about 25° C. The lithium ion battery of theExample 1 has a higher discharge specific capacity at the first cycle(about 55 mAh/g), and a better capacity retention. After 100 cycles ofthe charge and discharge, the discharge specific capacity of the lithiumion battery of the Example 1 is hardly decreased.

Example 2

In Example 2, the cathode composite material is prepared using the samemethod as in Example 1, except that the tetrabutyl titanate is replacedby zirconium n-butoxide. After the hydrothermal synthesis, the amorphousZrO₂ layer can be formed on the surface of the MnOOH, to form thecomposite precursor. After the lithiating step, the cathode compositematerial is the core-shell structure having LiMn₂O₄ as the core and Mndoped Li₂ZrO₃ as the shell.

Example 3

In Example 3, the cathode composite material is prepared using the samemethod as in Example 1, except that the tetrabutyl titanate is replacedby tetrabutyl orthostannate. After the hydrothermal synthesis, theamorphous SnO₂ layer can be formed on the surface of the MnOOH, to formthe composite precursor. After the lithiating step, the cathodecomposite material is the core-shell structure having LiMn₂O₄ as thecore and Mn doped Li₂SnO₃ as the shell.

Example 4

In Example 4, the cathode composite material is prepared using the samemethod as in Example 1, except that the tetrabutyl titanate is replacedby PbCl₄. After the hydrothermal synthesis, the amorphous PbO₂ layer canbe formed on the surface of the MnOOH, to form the composite precursor.After the lithiating step, the cathode composite material is thecore-shell structure having LiMn₂O₄ as the core and Mn doped Li₂PbO₃ asthe shell.

Example 5

In Example 5, the cathode composite material is prepared using the samemethod as in Example 1, except that the tetrabutyl titanate is replacedby TeCl₄. After the hydrothermal synthesis, the amorphous TeO₂ layer canbe formed on the surface of the MnOOH, to form the composite precursor.After the lithiating step, the cathode composite material is thecore-shell structure having LiMn₂O₄ as the core and Mn doped Li₂TeO₃ asthe shell.

Example 6

In Example 6, the cathode composite material is prepared using the samemethod as in Example 1, except that the tetrabutyl titanate is replacedby RuCl₄. After the hydrothermal synthesis, the amorphous RuO₂ layer canbe formed on the surface of the MnOOH, to form the composite precursor.After the lithiating step, the cathode composite material is thecore-shell structure having LiMn₂O₄ as the core and Mn doped Li₂RuO₃ asthe shell.

Example 7

In Example 7, the cathode composite material is prepared using the samemethod as in Example 1, except that the tetrabutyl titanate is replacedby HfCl₄. After the hydrothermal synthesis, the amorphous HfO₂ layer canbe formed on the surface of the MnOOH, to form the composite precursor.After the lithiating step, the cathode composite material is thecore-shell structure having LiMn₂O₄ as the core and Mn doped Li₂HfO₃ asthe shell.

Example 8

In Example 8, the cathode composite material is prepared using the samemethod as in Example 1, except that the tetrabutyl titanate is replacedby MnCl₄. After the hydrothermal synthesis, the amorphous MnO₂ layer canbe formed on the surface of the MnOOH, to form the composite precursor.After the lithiating step, the cathode composite material is thecore-shell structure having LiMn₂O₄ as the core and Mn doped Li₂MnO₃ asthe shell.

Examples for Doped Lithium Manganese Oxides

In these examples, the cathode composite material is prepared using thesame method as in Example 1, except that an amount of hydroxide of thedoping element L is added with the MnOOH. The doping element L is Co,Ni, Cr, V, I, Sn, Cu, Al, Fe, B, Sr, Ca, Ga, Nd, and Mg each in oneexample. A molar ratio of the doping element L and the MnOOH is abouty:(2−y). After the lithiating step, the cathode composite material isthe core-shell structure having Li_(x)Mn_(2-z)L_(z)O₄ as the core and Mndoped Li₂TiO₃ as the shell, wherein 0≦z<2, L is Co, Ni, Cr, V, I, Sn,Cu, Al, Fe, B, Sr, Ca, Ga, Nd, and Mg each in one example.

Depending on the embodiment, certain steps of methods described may beremoved, others may be added, and the sequence of steps may be altered.It is also to be understood that the description and the claims drawn toa method may include some indication in reference to certain steps.However, the indication used is only to be viewed for identificationpurposes and not as a suggestion as to an order for the steps.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the present disclosure.Variations may be made to the embodiments without departing from thespirit of the present disclosure as claimed. Elements associated withany of the above embodiments are envisioned to be associated with anyother embodiments. The above-described embodiments illustrate the scopeof the present disclosure but do not restrict the scope of the presentdisclosure.

What is claimed is:
 1. A cathode composite material comprising a cathodeactive material and a coating layer coated on a surface of the cathodeactive material, the cathode active material comprises a spinel typelithium manganese oxide, the coating layer comprises a lithium metaloxide having a crystal structure that belongs to C2/c space group of themonoclinic crystal system.
 2. The cathode composite material of claim 1,wherein a general formula of the lithium metal oxide is[Li_(1-2a)M_(a)□_(a)][Li_(1/3-2b-c)M_(b)N_(3c)A_(2/3-2c)□_(b)]O₂,wherein A represents a metal element having a +4 valence, M and Nrespectively represent doping chemical elements, “□” represents an atomvacancy occupying a Li site of [Li][Li_(1/3)A_(2/3)]O₂, 0≦2a<1,0≦2b+c<⅓, and 0≦2c<⅔.
 3. The cathode composite material of claim 2,wherein A is selected from the group consisting of Ti, Sn, Mn, Pb, Te,Ru, Hf, Zr, and any combination thereof.
 4. The cathode compositematerial of claim 2, wherein the M and N are respectively selected fromthe group consisting of alkali metal elements, alkaline-earth metalelements, Group-13 elements, Group-14 elements, transition metalelements, rare-earth elements, and any combination thereof.
 5. Thecathode composite material of claim 4, wherein M and N are respectivelyselected from the group consisting of Co, Mn, Ni, Cr, V, Ti, Sn, Cu, Al,Fe, B, Sr, Ca, Ga, Nd, Mg, and combinations thereof.
 6. The cathodecomposite material of claim 2, wherein at least one of M and N comesfrom the cathode active material.
 7. The cathode composite material ofclaim 2, wherein the general formula of the lithium metal oxide is[Li][Li_(1/3-c)Mn_(3c)A_(2/3-2c)]O₂.
 8. The cathode composite materialof claim 1, wherein the coating layer is a continuous layer and has auniform thickness.
 9. The cathode composite material of claim 1, whereinthe coating layer is an in situ formed layer on the surface of thecathode active material.
 10. The cathode composite material of claim 1,wherein a mass percentage of the coating layer is in a range from about0.05% to about 7%.
 11. The cathode composite material of claim 1,wherein a thickness of the coating layer is in a range from about 2nanometers to about 20 nanometers.
 12. The cathode composite material ofclaim 1, wherein the cathode active material comprises a plurality ofcathode active material particles, the coating layer is individuallycoated on the surface of each of the plurality of cathode activematerial particles.
 13. The cathode composite material of claim 12,wherein the coating layer completely coats an entire outer surface ofthe each of the plurality of cathode active material particles.
 14. Thecathode composite material of claim 1, wherein a size of the cathodeactive material is in a range from about 1 micron to about 500 microns.15. The cathode composite material of claim 1, wherein a shape ofcathode active material is selected from the group consisting of sphereshape, rod shape, needle shape, sheet shape, tube shape, and irregularshape.
 16. The cathode composite material of claim 14, wherein thecathode composite material has a shape corresponding to the shape of thecathode active material.
 17. The cathode composite material of claim 1,wherein the cathode active material and the coating layer are combinedby a chemical bonding force therebetween.
 18. The cathode compositematerial of claim 1, wherein the coating layer comprises a material thatis selected from the group consisting of Li₂TiO₃, Li₂MnO₃, Li₂SnO₃,Li₂PbO₃, Li₂TeO₃, Li₂RuO₃, Li₂HfO₃, Li₂ZrO₃, and combinations thereof.19. A lithium ion battery comprising: an anode electrode; a cathodeelectrode comprising a cathode composite material comprising a pluralityof cathode active material particles and a coating layer coated on asurface of each of the plurality of cathode active material particles,each of the plurality of cathode active material particles comprises aspinel type lithium manganese oxide, and the coating layer comprises alithium metal oxide having a crystal structure belonging to C2/c spacegroup of the monoclinic crystal system; and a non-aqueous electrolytedisposed between the cathode electrode and the anode electrode.